Photography in the analog as well as in the digital world allows for the representation of physical objects and their visual appearance. However, photography, including digital photography, has some drawbacks. Photography is not able to visualize dynamic interaction of light with surfaces, since it is a static method to capture light reflection of materials and objects. For example, this may be disadvantageous for the representation or documentation of any kind of surface structure, be it art-works, objects in forensics, dermatology, archaeology or for high quality product visualization (e.g., for promoting products).
RTI is a set of computational photographic methods that capture a subject's surface shape and color and enables the interactive re-lighting of the subject from any direction based on a mathematical model, such as Polynomial Texture Mapping (PTM). The reflection of light is, in a first step, captured by multiple photo images, where objects are illuminated by a light source from different positions (under different illumination angles). For example, the light source may be a flash light (or a LED light) which is synchronized with the digital camera to illuminate the static objects when a digital (source) image is recorded. In a second step, a polynomial of second order is fitted to the measured reflection for each pixel position. However, PTM has limitations of the mathematical model that is applied. A second order polynomial is able to reproduce reflection of diffuse (matte) surfaces, also called Lambertian surfaces, but reproduction of gloss is not possible.